1. Field of the Invention
The invention relates to a barrier layer structure and method of forming the structure for copper metallization.
2. Background of the Invention
Refractory metals and their nitrides have been used extensively as liner/barrier layers in aluminum metallization technology. For example, titanium and titanium nitride (Ti/TiN) are often used to improve adhesion and to minimize aluminum diffusion to underlying layers. However, in advanced integrated circuit fabrication, copper (Cu) and its alloys are increasingly being used for metal interconnects because they have lower resistivities and better electromigration characteristics than aluminum.
In forming copper metal interconnects in contact or via structures, a TiN barrier layer may be deposited by chemical vapor deposition (CVD) to provide conformal step coverage over the contact or via. A Cu layer is then formed on the TiN barrier, filling the contact or via. Thereafter, a planarization technique such as chemical mechanical polishing may be used to remove the Cu/TiN stack lying outside the contact or via, resulting in the formation of a planarized structure, which comprises a Cu plug inside the contact or via. In general, the Cu layer may be formed by electroplating, CVD or physical vapor deposition (PVD). In the case of electroplating, a relatively thin Cu seed layer is usually formed on the TiN barrier layer, in order to facilitate subsequent Cu electroplating.
Although CVD TiN provides conformal step coverage, PVD Ta and TaN are used as barrier materials in current Cu metallization technology, because a copper layer formed on a PVD Ta or TaN surface exhibits a good (111) orientation, which is desirable because it provides better resistance to electromigration and improved lifetime. Despite limited step coverage, the performance of PVD Ta or TaN as barrier layers is sufficient for current applications. For future applications, however, a CVD barrier layer is necessary to provide conformal step coverage. Thus, there is an ongoing need to form improved barrier layers suitable for future generations of Cu metallization.
The present invention relates to a barrier layer structure and a method of forming the structure for metallization. Embodiments of the invention provide a method of forming a first barrier layer using chemical vapor deposition, forming a second barrier layer using physical vapor deposition, and forming at least one copper layer on the second barrier layer.